1. Field of the Invention
This invention relates in general to magnetic heads, and more particularly to thin film magnetic heads and manufacturing methods therefor.
2. Description Relative to the Prior Art
Thin film magnetic heads have come into prominence because of their potential for manufacturing ease, especially in connection with the manufacture of high density multitrack heads. A thin film head is, typically, made by depositing a gap-defining non-magnetic film atop a magnetic substrate; then depositing a coil structure atop the non-magnetic film; and then depositing a magnetic film atop the coil structure. In the case of a thin film head used for, say, both recording and playback of video signals--or in the case of a thin film head used for microgap recording as taught in U.S. Pat. No. 4,302,790--a problem can arise depending on the coercivity of the recording medium with which the head in question is employed. For a high coercivity medium, the level of record flux may be in excess of the flux level at which the head poles magnetically saturate, thereby undesirably increasing the effective length of the head gap. U.S. patent application No. 374,665, assigned to the assignee hereof, and now abandoned, teaches that lining a transducer gap with high saturation material tends to preclude pole tip saturation; and it is to this technique that the invention is, perhaps, best compared.
Thin films as employed in connection with magnetic heads may be provided by a variety of techniques, most common of which is by sputtering. Sputtering, as is known, is a process by which ionic bombardment of a target results in the desired deposition of a thin film of target material upon a substrate. A mechanically hard, but magnetically soft, material which has found wide use in magnetic heads is the material known as Alfesil (also called Sendust), comprised of an alloy of iron, silicon, and aluminum. Alfesil--as target material--has been successfully sputtered; and has therefore been employed in the fabrication of thin film magnetic heads.
Given the tendency of closely spaced--and extremely thin--head poles to saturate while recording in a medium of high coercivity, it would be desirable to adapt the technique of abandoned U.S. patent application No. 374,665 to a thin film magnetic head comprised of Alfesil. Whereas the teaching of abandoned U.S. patent application No. 374,665 provides that a lining of Alfesil (or the like) be applied "in gap" to ferrite pole tips to lessen the chance of saturation of the ferrite pole tips, the present invention, as will appear below, calls for the modification of a thin film--during its formation--so as to cause that part of the thin film nearest the transducer gap of the head to exhibit greater saturation magnetization than other parts of the thin film. Such a technique would, therefore, have applicability both to the head of abandoned U.S. patent application No. 374,665, as well as to a thin film head as taught herein.
It has been found that, if a (negative) bias is applied to a substrate during the sputtering thereto of Alfesil, selective re-sputtering from the substrate film of aluminum and silicon will leave that film rich in iron and, attendantly, of higher saturation magnetization (17,000 gauss) than the starting material Alfesil (10,000 gauss). Such being the case, the invention provides that the sputtering of Alfesil-type material during the manufacture of a magnetic head be performed in two phases, first, while applying a bias of a first sense to a substrate to be sputtered upon, and, second, while applying a bias of different sense (e.g. a zero bias) to the substrate, thereby to cause a composite thin film to be formed on the substrate.